1. Field of the Invention
The invention relates to processes for preparing formaldehyde, glycolaldehyde and ethylene glycol, and more particularly to processes for preparing formaldehyde, glycolaldehyde and ethylene glycol by employing methanol.
2. Related Art
Ethylene glycol being a simple glycol is colorless, odorless and sweet liquid which can be mixed with water in any proportion. Ethylene glycol is used as solvents and raw materials for synthesizing polyester resins. Ethylene glycol is also used to manufacture antifreeze and thawing agents used in cars, planes and boats, or used to manufacture hydraulic brake, Inkpad and Ink used in pens and printing shops, etc.
In recent years, due to improved shale gas mining technology, a new process for preparing ethylene glycol by using ethylene in the shale gas is provided which comprises the followings steps: obtaining ethylene from shale gas; forming ethylene oxide (C2H4O) by reacting ethylene with oxygen in the presence of a silver (Ag) catalyst; forming ethylene glycol by reacting ethylene oxide with water in acid environment. Compared with the older process for preparing ethylene glycol, the cost of ethylene glycol prepared from the above-mentioned new process noticeably comes down and is about 0.7 USD/Kg. This causes a significant impact on those ethylene glycol producers located in the country or region that do not have the natural resources of shale gas.
Another process for preparing ethylene glycol is also provided which comprises the following steps. (a) Formaldehyde and water are formed by reacting methanol with oxygen at 300° C. in the presence of molybdenum (Mo) and iron (Fe) catalysts. (b) Anhydrous formaldehyde is obtained from the distillation of a mixture of the water and the formaldehyde at a pressure of about 4 kg/cm2G at a temperature of about 150° C. (c) Glycolaldehyde is obtained by reacting the formaldehyde with carbon monoxide and hydrogen in about 2 hours in the presence of xylene and a rhodium (Rh) catalyst at a temperature of about 100° C. at a pressure of about 150 kg/cm2G. In the step (c), the production and selectivity to glycolaldehyde is above 81% and 90%. For more information on the step (c), please refer to U.S. Pat. No. 7,511,178B2. (d) Ethylene glycol is obtained by reacting the glycolaldehyde with hydrogen in the presence of a nickel (Ni) catalyst at a temperature of about 40° C. at a pressure of about 50 kg/cm2G. In the step (d), the production to ethylene glycol product is above 90%. The cost of ethylene glycol prepared from this process is about 0.7 USD/Kg, which is close to the cost of ethylene glycol prepared from shale gas. However, this process needs more steps, and has to apply the reaction gases of different step in different reaction chambers. Since the production steps of this process are more complicated, this process cannot surpass the process of preparing ethylene glycol by using shale gas.
In view of this, an improved process for preparing ethylene glycol is needed which has simplified production steps and a reduced cost of preparing ethylene glycol, so that it can surpass the process of preparing ethylene glycol by using shale gas.